The distance a golf ball travels when struck by a golf club is determined in large part by club head speed at the point of impact with the golf ball. Club head speed in turn can be affected by the wind resistance or drag associated with the club head, especially given the large club head sizes of typical modern drivers. The club head of a driver, fairway wood, or metal wood in particular experiences significant aerodynamic drag during its swing path. The drag experienced by the club head leads to reduced club head speed and, therefore, reduced distance of travel of the golf ball after it has been struck.
Air flows in a direction opposite to the golf club head's trajectory over those surfaces of the golf club head that are roughly parallel to the direction of airflow. An important factor affecting drag is the behavior of the air flow's boundary layer. The “boundary layer” is a thin layer of air that lies very close to the surface of the club head during its motion. As the airflow moves over the surfaces, it encounters an increasing pressure. This increase in pressure is called an “adverse pressure gradient” because it causes the airflow to slow down and lose momentum. As the pressure continues to increase, the airflow continues to slow down until it reaches a speed of zero, at which point it separates from the surface. The air stream will hug the club head's surfaces until the loss of momentum in the airflow's boundary layer causes it to separate from the surface. The separation of the air streams from the surfaces results in a low pressure separation region behind the club head (i.e., at the trailing edge as defined relative to the direction of air flowing over the club head). This low pressure separation region creates pressure drag. The larger the separation region, the greater the pressure drag.
One way to reduce or minimize the size of the low pressure separation region is by providing a streamlined form that allows laminar flow to be maintained for as long as possible, thereby delaying or eliminating the separation of the laminar air stream from the club surface.
Reducing the drag of the club head not only at the point of impact, but also during the course of the entire downswing prior to the point of impact, would result in improved club head speed and increased distance of travel of the golf ball. When analyzing the swing of golfers, it has been noted that the heel/hosel region of the club head leads the swing during a significant portion of the downswing and that the ball striking face only leads the swing at (or immediately before) the point of impact with the golf ball. The phrase “leading the swing” is meant to describe that portion of the club head that faces the direction of swing trajectory. For purposes of discussion, the golf club and golf club head are considered to be at a 0° orientation when the ball striking face is leading the swing, i.e. at the point of impact. It has been noted that during a downswing, the golf club may be rotated by about 90° or more around the longitudinal axis of its shaft during the 90° of downswing prior to the point of impact with the golf ball.
During this final 90° portion of the downswing, the club head may be accelerated to approximately 65 miles per hour (mph) to over 100 mph, and in the case of some professional golfers, to as high as 140 mph. Further, as the speed of the club head increases, typically so does the drag acting on the club head. Thus, during this final 90° portion of the downswing, as the club head travels at speeds upwards of 100 mph, the drag force acting on the club head could significantly retard any further acceleration of the club head.
In actuality, during the course of the downswing, not only does the yaw angle vary, but also do the pitch and roll angles (although not to such a great degree as the yaw angle). Thus, club heads that have been designed to reduce the drag of the head at the point of impact, or from the point of view of the club face leading the swing, may not function well to reduce the drag during other phases of the swing cycle, such as when the heel/hosel region of the club head is leading the downswing.
It would be desirable to provide a golf club head that reduces or overcomes some or all of the difficulties inherent in prior known devices. Particular advantages will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of certain embodiments.